Modern hearing devices, in particular, hearing-aid devices, when employing different hearing programs (typically two to four; also referred to as audiophonic programs), permit their adaptation to varying acoustic environments, also referred to as acoustic scenes or acoustic situations. The idea is to optimize the effectiveness of the hearing device for the hearing device user in all situations.
The hearing program can be selected either via a remote control or by means of a selector switch on the hearing device itself. For many users, however, having to switch program settings is a nuisance, or it is difficult, or even impossible. It is also not always easy, even for experienced users of hearing devices, to determine, which program is suited best and offers optimum speech intellegibility at a certain point in time. An automatic recognition of the acoustic scene and a corresponding automatic switching of the program setting in the hearing device is therefore desirable.
The switch from one hearing program to another can also be considered a change in a transfer function of the hearing device, which transfer function describes how input audio signals generated by an input transducer unit of the hearing device relate to output audio signals to be fed to an output transducer unit of the hearing device.
There exist several different approaches to the automatic classification of acoustic environments (also referred to as acoustic surroundings). Typically, the methods concerned involve the extraction of different characteristics from an input signal. Based on the so-derived characteristics, a pattern-recognition unit employing a particular algorithm makes a determination as to the attribution of the analyzed signal to a specific acoustic environment.
As examples for classification methods and their application in hearing systems, the following publications shall be named: WO 01/20965 A2, WO 01/22790 A2 and WO 02/32208 A2.
Not in all acoustic environments, the program change based on the classification result provides for an optimum hearing sensation for the user. It is desirable to provide for an improved automatic adaptation of the transfer function of the hearing device to a current (actual) acoustic environment.
From U.S. Pat. No. 5,604,812, a hearing device is known, which, in absence of pre-stored hearing device settings, automatically and continuously adapts the transfer function by means of fuzzy logic. The results of such an approach may be unpredictable and might lead to undesired hearing device settings.
WO 99/65275 A1 discloses a device, e.g., a hearing device, with a signal processor, wherein parameters of the signal processor are directly steered in dependence of input signals.